1. Field of the Invention
This invention relates to primer compositions, and more particularly to primer compositions effective in enhancing the adhesion between a condensation type room temperature curable silicone elastomer and a coated metal.
2. Description of the Prior Art
Condensation type room temperature curable silicone elastomers are, in general, to some extent adhesive to metals. In practical use of the silicone elastomers, however, the metal surface is treated with a primer, before being coated. As a primer for such purpose, there has been known a primer containing a silane or a silicone resin which is a cohydrolytic condensation product of silane. Also, U.S. Pat. No. 483,9454 discloses a titano-organosilane compound and gives a description that the compound can be used as a primer. It is further described that the organosilane to be used is a tri- or tetra-alkoxysilane having the following formula: EQU R'.sub.4-x Si(OR).sub.x
wherein R and R' are each a monovalent hydrocarbon group, and x is 3 or 4, and that tri- or tetra-alkoxysilanes of the above formula are those in which all the alkoxy groups (OR) in the number of x are the same, and R' is a methacryloxypropyl group.
At present, coated metals are extensively used as outer walling material for buildings, in view of weatherability, appearance, etc., and coating materials based on fluororesin, urethane resin, acrylic resin or the like are used for the coating of metals. Condensation type room temperature curable silicone elastomers do not show good adhesion properties to metal substrates coated with the above coating materials, and the adhesion properties cannot be improved by use of a conventionally known primer. For instance, the primer disclosed in the aforementioned U.S. patent also does not exhibit good adhesion properties to coating materials based on fluororesin, urethane resin, acrylic resin or the like.